Histological subtyping and grading of malignancy are the cornerstone of the present World Health Organization (WHO) Classification of CNS tumors. However, among diffuse gliomas of the adult, patients with histologically identical tumors may have different outcomes. As the genomic analysis of these tumors has progressed, it has become clear that specific molecular features transcend histologically defined variants, and may become markers of prognostic and/or predictive value. At the present time, the number of molecular biomarkers with confirmed clinical relevance (MGMT promoter methylation, 1p/19q codeletion, IDH1/2 mutations) remains limited, but new technologies will hopefully provide new candidates requiring rigorous validation in well-designed clinical trials.